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On the phenomenology of yield in bisphenol‐a polycarbonate
Author(s) -
Stokes Vijay K.,
Bushko Wit C.
Publication year - 1995
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760350403
Subject(s) - materials science , necking , polycarbonate , composite material , ultimate tensile strength , creep , tensile testing , strain rate , stress (linguistics) , yield (engineering) , linguistics , philosophy
The phenomenology of yield in bisphenol‐A polycarbonate is explored through tensile tests on thin rectangular specimens and through pressure‐induced bulging of thin, clamped circular disks. In a tensile test, while the nominal critical stress at which yield initiates and the nominal draw stress at which a stable neck propagates along a specimen depend on the temperature and the strain rate, the ratio of the draw stress to the critical stress is shown to be approximately 0.75 over a temperature range of 22 to 65°C and strain‐rates in the range of 10 −4 to 10 0 s −1 . Specimens subjected to constant tensile loads between the draw and critical stresses are shown first to creep till stretches on the order of 1.06 are attained and then are shown to undergo stable necking. Tensile tests on thin, wide rectangular specimens show that yielding initiates through shear bands that broaden and intersect to generate necks, which subsequently propagate along the specimen. In pressure‐induced bulging of clamped disks, biaxial stretching progresses monotonically under increasing pressures; strain localization does occur near the outer edges of the specimens, however. Heating of a specimen with a substantial stably necked region shows that the temperature‐induced recovery of the specimen from its deformed state begins well below the transition temperature T g of the material, although most of the recovery occurs at T g .